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1、Environmental Impacts of Solid Waste LandfillingAbstract:Inevitable consequences of the practice of solid waste disposal in landfills are gas and leachate generation due primarily to microbial decomposition, climatic conditions, refuse characteristics and landfilling operations. The migration of gas
2、 and leachate away from the landfill boundaries and their release into the surrounding environment present serious environmental concerns at both existing and new facilities. Besides potential health hazards, these concerns include, and are not limited to, fires and explosions, vegetation damage, un
3、pleasant odors, landfill settlement, ground water pollution, air pollution and global warming. This paper presents an overview of gas and leachate formation mechanisms in landfills and their adverse environmental impacts, and describes control methods to eliminate or minimize these impacts. Keywords
4、: landfill, solid waste disposal, biodegradation, gas and leachate generation, environmental impacts, control methods1.Introduction Solid waste disposal in landfills remains the most economic form of disposal in the vast majority of cases (Thompson and Zandi, 1975; Rushbrook, 1983; Carr and Cossu, 1
5、990). Therefore, landfills will continue to be the most attractive disposal route for solid waste. Indeed, depending on location, up to 95% of solid waste generated world- wide is currently disposed of in landfills (Bingemer and Crutzen, 1987; Cossu, 1989; Nozhevnikova et al., 1992; Gendebien et al.
6、, 1992). Alternatives to landfilling are considered as volume reduction processes because they produce waste fractions (e.g.ashes and slag from combustion processes that represent the second leading method of waste disposal) which ultimately must be landfilled (Emberton and Parker, 1987). Resorting
7、to landfills is not limited to the disposal of municipal solid waste, but it icludes most other industrial wastes. For instance, nearly 80% of hazardous wastes generated in the U.S. is dumped in landfills (Eichenberger et al., 1978). Solid waste composition varies substantially with socio-economic c
8、onditions, location, Most organic materials are biodegredable and can be broken down into simpler compounds by aerobic and anaerobic microorganisms, leading to the formation of gas and leachate. The following sections provide an overview of the mechanisms of gas and leachate formation in landlls, th
9、eir environmental impacts, and appropriate control methods to eliminate or minimize these impacts.2. Landll Gas Formation MechanismsAt the time of waste deposition in a landll, oxygen is present in the void space, giving rise to aerobic decomposition during which biodegradable organic materials reac
10、t quickly with oxygen to form carbon dioxide, water, and other by-products (e.g. bacterialcells). Carbon dioxide is produced in approximate molar equivalents to the oxygenconsumed. Oxygen depletion within the landll marks the onset of the anaerobic decompositon phase. Although a landll ecosystem und
11、ergoes an initial short aerobicdecomposition phase, the subsequent anaerobic phase is the dominant phase in its age and the more important one from the perspective of gas formation.Much of what is known or assumed concerning anaerobic processes in landlls has primarily come from work with anaerobic
12、digesters. Microbial populations in both environments appear to be similar however, the major dierence is that the substrates may vary in their relative content of fat, protein, and carbohydrates, and conversely to landlls, the environment in anaerobic digesters is well controlled and often under op
13、timal conditions.Investigators have recognized several major steps to describe the anaerobic de-composition phase during which organic materials are converted to methane and carbon dioxide (Alexander, 1971; Zehnder, 1978; Wolfe, 1979; McCarty 1981; Zehnder et al.,1982; Mosey, 1983; Archer and Robert
14、son, 1986; Balba, 1987). These steps are highly inter-dependent and include hydrolysis, acidogenesis, acetogenesis, and methanogenesis(Figure 1).Generally, the breakdown of organic matter in anaerobic ecosystems proceedssequentially from the complex to the simple starting with the hydrolysis of comp
15、lex particulate matter to simpler polymers like proteins, carbohydrates and lipids which are further hydrolyzed to yield biomonomers like amino acids, sugars, and high molecular fatty acids. Amino acids and sugars are converted into either intermediate by-products (e.g. propionic, butyric and other
16、volatile acids) or directly fermented to acetic acid. High molecular fatty acids are oxidized to intermediate by-products and hydrogen. Methane and carbon dioxide generation occurs primarily through acetate cleavage. Methane is also produced through carbon dioxide reduction with hydrogen.In a landll environment, methane generation from the latter route is often limited bythe lack of hydrogen which is consumed by sulfate reducers (Kasali, 1986).Qualitatively, landll gas is
